Quick answer
Newton's second law gives F = m a. A 10 kg mass accelerated at 2.5 m/s² needs 25 N; its weight on Earth is 98.07 N.
Enter mass and acceleration. The calculator returns the force and the weight of the mass.
Related tools: Centripetal Force Calculator: Force and acceleration for circular motion. Normal Force Calculator: Normal force on an object resting on a flat or inclined surface. Net Force Calculator: Resultant of several forces at different angles.
How to use the Force Calculator
- Enter mass (kg) (above 0).
- Enter acceleration (m/s²).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Mass | A number, in kg | > 0 |
| Acceleration | A number, in m/s² | — |
Formula and method
Formula
F = m a
IEEE-754 double precision; shown to the decimals indicated.
Weight uses standard gravity 9.80665 m/s².
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Mass = 10; Acceleration = 2.5.
| Result | Value |
|---|---|
| Force | 25 N |
| Weight of the mass | 98.0665 N |
Example 2
Inputs: Mass = 1500; Acceleration = 3.
| Result | Value |
|---|---|
| Force | 4,500 N |
| Weight of the mass | 14,709.975 N |
Example 3
Inputs: Mass = 0.2; Acceleration = 9.80665.
| Result | Value |
|---|---|
| Force | 1.96133 N |
| Weight of the mass | 1.96133 N |
The first line is the headline result (force). Below it the force Calculator lists weight of the mass, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Net force
The force here is the net force when several forces act. If friction opposes motion, the applied force must be larger than m·a. Weight is the special case F = mg with a = 9.80665 m/s².
Units
1 newton accelerates 1 kg at 1 m/s². 1 N is about the weight of a small apple. Mass in kg and acceleration in m/s² give force in newtons; 1 lbf is 4.448 N.
How the result changes with mass
Holding every other input at the first worked example, this table changes only mass. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Mass | Force | Weight of the mass |
|---|---|---|
| 5 | 12.5 N | 49.03325 N |
| 10 | 25 N | 98.0665 N |
| 20 | 50 N | 196.133 N |
| 40 | 100 N | 392.266 N |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Mass: entering "0" shows "Mass must be greater than 0." beside that field and no result.
- Acceleration: left empty shows "Enter acceleration." beside that field and no result.
Choosing between the Force Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Centripetal Force Calculator](/science/centripetal-force-calculator/) | mass, speed and radius | Centripetal force |
| [Normal Force Calculator](/science/normal-force/) | mass, incline angle and gravitational acceleration | Normal force |
| [Net Force Calculator](/science/net-force-calculator/) | force magnitudes and direction of each force | Net force |
| [Friction Force Calculator](/science/friction-force-calculator/) | coefficient of friction μ and normal force | Friction force |
| [Force Converter](/converters/force-converter/) | value, from and to | Pound-force (lbf) → Newton (N) |
Background: motion and mechanics
For constant acceleration the standard relations are v = u + at, s = ut + ½at², v² = u² + 2as and s = ½(u + v)t. Pick the equation that contains your three known quantities and the one you want. Use SI units (metres, seconds, kilograms, newtons, joules) throughout or the answer will be off by a factor.
These equations stop applying when acceleration changes during the motion, as with a rocket burning fuel; that needs calculus or numerical methods.
Assumptions and limitations
- Net force when several forces act
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for mass and acceleration to confirm this.
Frequently asked questions
What is the force to accelerate a 1,000 kg car at 3 m/s²?
F = ma = 1,000 × 3 = 3,000 N.
Is weight a force?
Yes. Weight is the gravitational force on a mass, W = mg; a 10 kg mass weighs about 98.07 N.
What is the unit of force?
The newton (N): 1 N accelerates 1 kg at 1 m/s².
What does the Force Calculator calculate?
Force from mass and acceleration (Newton's second law). It returns Force and Weight of the mass.
What formula does the Force Calculator use?
F = m a. Weight uses standard gravity 9.80665 m/s².
What do I need to enter in the force Calculator?
You enter Mass (kg) and Acceleration (m/s²).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Net force when several forces act.
What is an example of a force result?
With mass 10 and acceleration 2.5, the force is 25 N.
Related calculators
- Centripetal Force Calculator — Force and acceleration for circular motion.
- Normal Force Calculator — Normal force on an object resting on a flat or inclined surface.
- Net Force Calculator — Resultant of several forces at different angles.
- Friction Force Calculator — Friction force from the coefficient of friction and the normal force.
- Force Converter — Convert newtons, pounds-force, kilograms-force and dynes.
- Gravitational Force Calculator — Newtonian gravitational attraction between two masses.
- Impulse Calculator — Impulse from force and time, and the change in velocity if the mass is known.
Sources
- CODATA 2018 / SI exact constants: g₀ = 9.80665 m/s², c = 299,792,458 m/s, h = 6.62607015×10⁻³⁴ J·s, e = 1.602176634×10⁻¹⁹ C, G = 6.67430×10⁻¹¹ m³/(kg·s²)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.